Herein are described fuser members useful in electrostatographic apparatuses, including printers, copiers, image-on-image, digital, and other apparatuses. More specifically, described are compositions and processes which are effective in minimizing or eliminating volatile emissions from the heated fuser oil composition during thermal and/or pressure fusing operations. The compositions which are particularly effective as volatile emission inhibitors or suppressants and as release agents for a variety of metal, elastomeric, or composite fuser substrates contain blends comprising a mercapto functional release agent and a polydimethylsiloxane fuser agent comprising fluoro-functional groups.
The use of polymeric release agents having functional groups, which interact with a fuser member to form a thermally stable, renewable self-cleaning layer having good release properties for electroscopic thermoplastic resin toners, is described in U.S. Pat. Nos. 4,029,827; 4,101,686; and 4,185,140, the disclosures each of which are incorporated by reference herein in their entirety. Disclosed in U.S. Pat. No. 4,029,827 is the use of polyorganosiloxanes having mercapto functionality as release agents. U.S. Pat. Nos. 4,101,686 and 4,185,140 are directed to polymeric release agents having functional groups such as carboxy, hydroxy, epoxy, amino, isocyanate, thioether and mercapto groups as release fluids. U.S. Pat. No. 5,716,747 discloses the use of fluorine-containing silicone oils for use on fixing rollers with outermost layers of ethylene tetrafluoride perfluoro alkoxyethylene copolymer, polytetrafluoroethylene and polyfluoroethylenepropylene copolymer. U.S. Pat. No. 5,698,320 discloses the use of fluorosilicone polymers for use on fixing rollers with outermost layers of perfluoroalkoxy and tetrafluoroethylene resins.
Examples of release agents for fuser members are nonfunctional silicone release oils, mercapto-functional silicone release oils, and amino-functional silicone release oils. However, depending on the type of outer layer of the fuser member chosen, there may be several drawbacks to using nonfunctional, mercapto-functional, or amino-functional silicone oils as release agents. For example, for silicone rubber outer layers, the silicone release agents provide adequate wetting of the silicone rubber surface. However, the nonfunctional and functional silicone release agents can swell the silicone rubber coating. Swelling shortens roll life because it weakens the silicone, resulting in rapid mechanical wear. High viscosity (13,000 cS) nonfunctional fluids are currently used with silicone rolls, because these fluids do not swell the rolls as much as lower viscosity (100-350 cS) oils. However, high viscosity oils present fluid management problems and do not wet the fuser as efficiently.
On the other hand, fluoroelastomers used as an outer coating for fuser members are more durable and abrasion resistant than silicone rubber fuser members. Also, fluoroelastomer outer coatings do not swell when contacted by nonfunctional or functional silicone fluids. Therefore, fluoroelastomers are the current desired outer fuser member coating.
Various compositions have been proposed for treating fuser roll and belt substrates to impart release properties thereto. However, many of these compositions, in particular those comprised of organopolysiloxanes and various derivatives thereof, suffer from thermal instability when heated to fusing temperatures, for example about 150° C. and above for short periods of time of, for example, about 0.5 seconds and longer. Thermal degradation of organopolysiloxane release agents, such as dimethylsilicone oils and related derivatives may result in the generation of volatile byproducts, for example, formaldehyde (CH2═O), formic acid (HCO2H), carbon dioxide (CO2), carbon monoxide (CO), hydrogen (H2), methanol (CH3OH), ammonia (NH3), hydrogen sulfide (H2S), trifluoropropionaldehyde (CF3CH2CH═O), and the like, which byproducts have potentially objectionable odor and may be mucousal irritants in the ambient environment of an operating xerographic machine. The byproducts may also be harmful to machine components and subsystems, such as photoreceptor or fuser members, promoting premature failure. Further, the byproducts may remain dissolved in the release agent oil and may promote continued or accelerated degradation of the silicone release agent oil composition thereby leading to undesirable changes in release agent viscosity, release properties, and perhaps negatively impacting optimal fusing performance of the fusing subsystem. The volatile emissions also have an unpleasant odor and are potentially hazardous to machine operators or passersby, particularly with prolonged exposure. Volatile emissions from fused copy or prints, that is volatiles that are dissolved in the release agent oil, may become imbibed into paper fibers, synthetic receiver sheet materials, or fixed toner images, and may outgas over time and may further pose an objectionable odor or irritation problem which may lead to reduced customer acceptance and satisfaction.
Other sources of volatile emission components include residuals from preparative reactions or purification processes residing in the oil itself, such as solvents, monomers, initiators, impurities, and the like; and degradation products arising from various oil performance additives. Commercial manufacturers and suppliers of silicone release agent oil products routinely employ additional processing steps to purposely “devolatilize” their products in recognition of volatile emissions being a problem for corrosion or contamination of mechanical and electrical machine components.
Antioxidant additives for silicone fluids are known. J. M. Nielsen in “Stabilization of Polymers and Stabilizer Processes”, Advances in Chemistry Series, Vol. 85, American Chemical Society, Washington D.C., 1968, provides an early account of antioxidant additives for silicone fluids including, for example, redox metal complexes and soaps which are however disadvantaged by producing haze, gels or sludge on storage and or during use, and interfering with copy quality and color print fidelity.
T. S. Heu in Journal of the Korean Rubber Society, Vol. 18, No. 1, pages 21 to 29 (1983) describes the stability and degradation prevention of silicone oils and rubbers. Silicone compound stability is categorized into oxidation stability and thermal stability. Oxidation stability refers to resistance of the silicone compound to react with oxygen which reactions lead to intermolecular cross-linking and increased viscosity for silicone liquids and hardening for silicone rubbers. Thermal stability refers to the resistance of the silicone compound to undergo intramolecular cleavage of siloxane bonds (Si—O—Si) by heat, which reactions produce lower molecular weight products and leads to reduced viscosity for silicone oils and softening of silicone rubbers. Resistance to both pathways of degradation is called thermal oxidation stability. Homologous hydrocarbon structural derivatives of dimethyl polysiloxanes such as ethyl, propyl, butyl, and the like, generally possess lower thermal stability than the dimethyl compound. Certain structural derivatives of polysiloxanes have enhanced thermal stability, for example, phenyl methyl siloxane, but these derivatives are disadvantaged by their higher cost and thermal degradation liberates benzene. Thermal stability for silicone oils having the same repeat unit is generally higher for the oil with the greater molecular weight.
Additives made from, for example, salts of organometallic acids are commonly used to improve the thermal oxidation stability of silicone oils. However, these salts chemically react with the silicone oil in a multitude of ways as part of the stabilization mechanism and therefore unpredictably lead to oils having significantly altered physical, for example, viscosity and performance, for example, release properties.
U.S. Pat. No. 4,029,827, to Imperial et al, discloses polyorganosiloxanes having functional mercapto groups, which are applied to a heated fuser member in an electrostatic reproducing apparatus to form a thermally stable, renewable, self-cleaning layer having superior toner release properties for electroscopic thermoplastic resin toners.
U.S. Pat. No. 5,217,837 discloses a release agent having functional groups.
U.S. Pat. No. 5,366,772 discloses a fuser member with a hybrid polymeric network outer layer comprising a haloelastomer, coupling agent, functional polyorganosiloxane and crosslinking agent.
U.S. Pat. No. 4,251,277, to Martin, discloses compositions containing organopolysiloxanes and thiofunctional polysiloxanes having at least one mercaptan group, which are effective as corrosion inhibitors and as release agents for metal substrates.
U.S. Pat. No. 4,515,884 to Field et al, discloses a method of fusing by providing a silicone elastomer fusing surface, heating the fuser member to fuse toner particles to the receiver substrate, applying directly to the silicone elastomer fusing surface in non-emulsified form an unblended polydimethylsiloxane having a viscosity of about 7,000 to about 20,000 centistokes, and contacting the toner image on the substrate with the toner release agent which includes an unblended polydimethyl siloxane.
U.S. Pat. No. 5,395,725 to Bluett, et al, discloses use of mercapto-functional fuser agent to non-mercapto release agent to reduce formaldehyde emissions, wherein the non-mercapto release agent may be amino-functional, phenyl-methyl siloxane, trifluoropropyl-functional, or non-functional polydimethylsiloxane release agent.
U.S. Pat. No. 6,197,989 B1 to Furukawa et al. discloses a fluorine-containing organic silicone compound represented by a formula.
U.S. Pat. No. 5,757,214 to Kato et al. discloses a method for forming color images by applying a compound which contains a fluorine atoms and/or silicon atom to the surface of electrophotographic light-sensitive elements.
U.S. Pat. No. 5,716,747 to Uneme et al. discloses a fluororesin coated fixing device with a coating of a fluorine containing silicone oil.
U.S. Pat. No. 5,698,320 to Ebisu et al. discloses a fixing device coated with a fluororesin, and having a fluorosilicone polymer release agent.
U.S. Pat. No. 5,636,012 to Uneme et al. discloses a fixing device having a fluororesin layer surface, and using a fluorine-containing silicone oil as a repellant oil.
U.S. Pat. No. 5,627,000 to Yamazaki et al. discloses a fixing method having a silicone oil coated on the surface of the heat member, wherein the silicone oil is a fluorine-containing silicone oil and has a specific formula.
U.S. Pat. No. 5,624,780 to Nishimori et al. discloses a fixing member having a fluorine-containing silicone oil coated thereon, wherein the silicone oil has a specific formula.
U.S. Pat. No. 5,568,239 to Furukawa et al. discloses a stain proofing oil for heat fixing, wherein the fluorine-containing oil has a specific formula.
U.S. Pat. No. 4,968,766 to Kendziorski discloses a fluorosilicone polymer for coating compositions for longer bath life.
In electrostatic and xerographic applications, it is desirable to use release agent oils which are cost effective; clear; colorless; odorless or nearly so at room temperature and at fuser operating temperatures; free of additives such as acids, bases, peroxides, heavy metals, and the like, that can interfere with the fusing and sheet release performance of the fusing system and associated hardware; and free of or produce minimal volatile emission component(s) over the service life of the release agent oil.
A mercapto functional release agent has been found, which decreases or eliminates the production of formaldehyde byproducts. In fact, U.S. Pat. No. 5,395,725 to Bluett, et al., described above, teaches the addition of mercaptopropyl functional fuser agent to polydimethyl siloxanes and aminopropyl-substituted polydimethyl siloxanes to inhibit the formation of formaldehyde.
In the case of fluorofunctional organopolysiloxane fuser release fluids, there remains a need for improved oxidative or thermal stability to minimize or eliminate the emission of potentially hazardous volatile compounds, such as fluoroaldehydes, at fuser operating temperatures. It is desirable to achieve the need without diminishing the release properties of the oil or compromising the print quality.